This invention relates to an improved nutating earth drilling bit for use in drilling systems in which the drilling fluid and cuttings are lifted to the surface within the drill string, rather than in the annular space between the drill string and the hole wall (the hole annulus) and which is primarily intended for the drilling of hard formations.
In single tube drilling systems utilizing conventional circulation, a drilling fluid (e.g., mud or water) is pumped through the drill string to the bit, and returns to the surface in the hole annulus. Nutating drill bits for conventional circulation drilling systems have been known for a number of years. See, for example, Campbell U.S. Pat. No. 1,954,166, Thaheld U.S. Pat. No. 2,020,625, Zublin U.S. Pat. Nos. 2,025,260 and 2,275,832, and Bennett U.S. Pat. No. 3,429,390. In such drilling bits, the axis of rotation of the freely rotating cutting member is formed at a relatively small angle with respect to the axis of rotation of the drill string and the hole being produced by the bit. As a result, the cutting member slowly retrogresses with respect to the drill string's rotation and undergoes nutational action.
Dual concentric drill pipe is employed in a number of drilling systems in which the drilling fluid and cuttings are transported to the surface inside the drill string rather than in the hole annulus. This type of drill pipe, which is described in Henderson U.S. Pat. No. 3,208,539, has an inner tube concentrically disposed within an outer pipe, thus defining a continuous annular flow passage between the two tubular members (the pipe annulus or annular conduit) and a continuous cylindrical flow passage through the inner tube (the central conduit). In enclosed circulation drill systems, the annular conduit delivers drilling fluid (e.g., mud, water, etc.) from the surface to the bit and the central conduit carries the drilling fluid and entrained cuttings from the bit to the surface.